Method of securing metal contacts to carbon electrodes.



S. BENKU.

METHOD OF SECURING METAL CONTACTS T0 CARBON ELEGTRODES. APPLIOATIONFILED JULY 3, 1909.

942,704. Patented Dec. 7, 1909.

E 1 flg4 o O 9 o Ey2 w & 0

C/G/C C O 7 2d a .4 W64 CZ STEPHAN. BENKO, OF BUDAPEST, AUSTRIA-HUNGARY.

METHOD OF SECURING METAL CONTACTS TO CARBON ELEOTRODES.

Specification of Letters Patent.

Patented Dec. 7, 1909.

Application filed. July 8, 1909. Serial No. 506,610.

To all whom it may concern:

Be it known that I, STEPHAN BENKo, a subject of the King of Hungary,residing at Budapest, in Austria-Hungary, have invented a certain newand useful Improved Method of Securing Metal Contacts to CarbonElectrodes, of which the following is a specification.

The most suitable negative electrode for obtaining a strong current inthe case of galvanic elements is, as is well known, the carbon electrodefirst used by Bunsen. All elements provided with carbon electrodes have,however, the essential disadvantage that there isproduced a considerableinternal (terminal) resistance between the metal pole *mounted onthehead portion of the carbon application Serial No. 473,047. In theseelements there is produced a constant and very considerable quantity ofcurrent which, more particularly in large elements, cannot be carriedaway by means of ordinary binding screw terminals or the like, without aconsiderable loss of energy and moreover a considerable heating can beobserved on such terminals. In the above mentioned carbon electrodescare must be therefore taken not only to enable the great quantity ofcurrent produced to be carried away from the generating electrode, butalso to cause the depolarizing gas or the electrolyte to penetrate intoall the pores for the purpose of obtaining a constant current. This can,however, be done in a reliable manner only when the opening of thecarbon recess or hollow is closed in a complete, that is to say airandliquid-tight manner, as otherwise a great portion of the gaseous orliquid substance gets lostowing to incomplete joint or instead ofpassing nto the pores, escapes throu h the incomplete joint.

In orderto get a better contact between the carbon and the contactmetal, it has already been suggested to melt the contact metal and todip the carbon into the same.

It was in that case necessary, more particularly when using lead ascontact metal, to close the pores of the carbon by means of paraflin, inorder to prevent the electrolyte from getting between the carbon and themetal, and in the case of, say, lead and an electrolyte containingsulfuric acid, being used, to avoid formation of sulfate of lead.Moreover, in all well known processes only a superficial contact isproduced between carbon and metal, which is not sufiicient either forforming a tight joint or for avoiding the above mentioned drawbacks.

According to this invention, the carbon is impregnated at the headportion which is to be provided with metal contact, with a metal whichcannot be decomposed by the electrolyte. The metal is incorporated withthe carbon by suction or by forcing it in in a liquid state.

In carrying out the process in practice, the carbon is, for instance,heated to a point above the melting pointof the'contact metal beforedipping it into the latter. In that way air is expelled from the poresof the carbon and the pores deprived of air, get filled with the contactmetal on being dipped into it. On solidifying, the contact metalpenetrates into the pores and completely fills them up, so that noelectrolyte can pass between the carbon and the metal. A formation ofsulfate of lead if lead is used can therefore take place only within thepores, where however it is harmless. The result is that the contactitself can be formed by a metal which is decomposed by the electrolyteas the decomposition takes place only in the pores whereit is harmless.

In order to compress the porous contact metalafter casting, and toinsure its adhesion to the carbon, the end of the carbon provided withthe contact, is placed under a very high pressure, the lateral walls ofthe mold being obliged to yield to the outer pressure. The mold can bemade for in-' stance in such way that two of its lateral walls areadjustable by means of a dove-tail guide or the like, while the bottomand cover plates, as well as the remaining lateral walls are fixed. Theadjustable lateral walls are brought nearer together during thecompression, the press-jaws of a vise engaging, say, direct with thelateral walls of the mold. Although it has been already attempted to putfinished, cast-on-contacts, under pressure, by shrinkin on metal rings,the compression in a mo d has the advantage that the pressure can beexercised already when the metal is in a semi-liquid state.

In the accompanying drawing z Figure 1 is a cross-sectional elevation ofFig. 2. Fig. 2 is a side elevation of a hollow carbon body; Fig. 3 is aperspective view of the same; Fig. 4 is an elevation of a carbon bodysuspended in a mold; Fig. 5 is a perspective view of the mold; Fig. 6 isa section showing a hollow carbon body after casting; Fig. 7

is a similar view of a solid body, and Fig. 8 is a section showing amodified arrangement applied to a hollow carbon body.

The metal contact forming the subject of the invention is produced inthe following manner: A hollow carbon body I), say of rectangular shape,is provided near its free opening with perforations a passing throughboth its' lateral walls. The carbon body is placed or suspended in amold 0 in the manner shown in Fig. 1, with the perforations downward.The suspension must be effected in such manner that the carbonbodyshould not reach the bottomof the mold, but that the edge of the lattershould cover the openings a. After the carbon, as well as the mold, hasbeen heated in accordance with this invention, namely to a point abovethe melting point of the contact metal, the molten metal is poured intothe mold. Lead, hard lead, aluminium etc. are specially suitable forcasting. On cooling and. solidifying, the metal contracts, which resultsin its adhering firmly to the carbon body. The metal rods produced inand between the openings 0, exercise a strong tension. The final,complete and firm contact between the carbon body and the metal cast on,isobtained by ex osing the carbon head provided with still so t,semi-liquid, warm metal to a pressure of 30 to 100 atmospheres, and ifdesired leaving it under that pressure until the metal has completelysolidified. This pressure may be exercised on the lateral surfaces ofthe carbon by means of a parallel vise, a hydraulic press or the like bymeans of solid jaws. The pressure is stilhfurther increased in thedirection of the axis of the metal rods produced in the holes a (seearrows in-Figs. 6 and 7 and in that way the metal is forced into theinner pores of the carbon.

The action of the process consists in the metal contact so to saymelting together with the carbon body and adhering to it so that itcan-be removed only by melting it off. The result is that the loss ofelectrical pressure in the element is reduced, and that in hollow carbonbodies an airand liquid-tight closing is obtained at the same timeandthat finally the efliciency of the element is indirectly increased;

The screws d shown in Fig. 8 are intended on the one hand for carryingthe current from the pole into the conductor, and on the other hand,they avoid the weakening of contact which is possible in the caseof somemetals (for instance, lead). The perforations for these tension screwsare made in such manner that the metal rods produced in the holes a areperforated. Care must be taken during that operation that the drillshould not touch the wall of the carbon, but pass only through themetal, as otherwise the tension screws 1 would come into contact withthe electrolyte drawn in and thus become corroded and dissolved. Forthat reason, the metal contact must be made of some metal resistingacids, thus for instance when chromic acid alone is used. of lead oraluminium, and when using chromic acid with an excess of sulfuric acid,of lead only.

In the case of metals with a very high melting point, the liquid metalis drawn in into thecarbon. This process is more particularly suitablewhen making contacts of a metal that does not resist acids, or of amixture of a metal that does, and a metal that does not, resist acids,for in that case the carbon must be impregnated through and through withthe metal.

What I claim as my invention and desire to secure by Letters Patentis 1. A method of attaching metal contacts to carbon electrodes,consisting in heating the head portion of the electrode to a temperatureabove the melting-point of the metal to be employed, and in impregnatinelectrodes at the parts to wh1ch the metal contact is to be attached,with perforations, placing the perforated parts of the electrodes, in aheated state, into a mold, ouring molten metal into the mold, and sujecting the cast portion to a high pressure.

4. A method of securing metal contacts to carbon electrodes consistingin providing the electrodes, at the parts to wh1ch the metal contact isto be attached, with perforations, placing the perforated parts of theelectrodes in a heated state into a mold, pouring molten .metal into themold, and sub ecting the cast portion together with the mold, to a highpressure. a

5. A method of securing metal contacts to carbon electrodes consistingin providing the electrodes, at the parts to which the metal contact isto be attached, tvith perforations, I In testimony whereof have signedmy placing the perforated parts. of the elecname to this spec ficatlon1n the presence of trodes in a heated state, into a mold, pouring twosubscribing witnesses.

molten metal into the mold, and subjecting STEPHAN BENKG. 5 the castportion together with the mold to Witnessesa high pressure in thelongitudinal direction JOSEPH WIRKMANN,

of said perforations. MICHAEL Tomlin.

